Updated

A gleeful, laughing Usama bin Laden described the joy he felt when he learned his plan to destroy the World Trade Center had succeeded — and more than 3,000 people had been murdered — on a videotape released by the Pentagon Thursday.

Bin Laden, smirking and remorseless, told associates on the videotape that he had advance knowledge of the plan to hijack airliners and smash them into the Twin Towers and the Pentagon. A fourth airliner that was heading toward Washington crashed in western Pennsylvania.

U.S. officials said the chilling videotape proves that bin Laden was the mastermind behind the Sept. 11 terror attacks.

Bin Laden called the hijackings a "martyrdom operation," and said the men who carried them out didn't know the precise details until just before they boarded the planes.

He recalled tuning in to the radio to hear American news broadcasts of the attack.

"They were overjoyed when the first plane hit the building," he said of others listening with him that day. "So I said to them: Be patient."

He said, "At the end of the newscast, they reported that a plane just hit the World Trade Center."

"Allah be praised," replied one of the other men in the videotape.

"After a little while, they announced that another plane had hit the World Trade Center," bin Laden recalled. "The brothers who heard the news were overjoyed by it."

The video, apparently not intended for public viewing, records a meal and conversation between bin Laden and a Saudi Arabian sheik, a prominent cleric whom officials have declined to identify. At one point, the sheik kisses bin Laden on the forehead — a sign of great respect in the Muslim world.

On the tape, bin Laden said "we calculated in advance" the number of casualties in the Sept. 11 attacks.

"We calculated that the floors that would be hit would be three or four floors; I was the most optimistic of them all.

"Due to my experience in this field, I was thinking that the fire from the gas in the plane would melt the iron structure of the building and collapse the area where the plane hit and all the floors above it only. This was all that we had hoped for."

He said Mohammed Atta was the leader of the suicide hijackers, and that the terrorists did not know the details of the plan until just before they boarded the planes.

"The brothers who conducted the operation, all they knew was that they have a martyrdom operation and we asked each of them to go to America, but they didn't know anything about the operation, not even one letter," bin Laden said.

"But they were trained and we did not reveal the operation to them until they are there and just before they boarded the plane," he added.

With a smile on his face, bin Laden said those trained to fly didn't know the other hijackers in the group.

"One group of people didn't know the other," he said.

Two bin Laden associates — spiritual adviser Ayman al-Zawahri and spokesman Abu Ghaith — also appear in the tape.

On the tape, bin Laden is sitting on the floor of a spare room, talking with the other men.

Entering the room, bin Laden bends over to greet the sheik, then smilingly takes his place next to him, sitting cross-legged on the floor.

The sheik promptly thanks bin Laden, saying, "You have given us weapons, you have given us hope and we thank Allah for you."

"Everybody praises what you did, the great action you did, which was first and foremost by the grace of Allah," the sheik continued. "This is the guidance of Allah and the blessed fruit of Jihad."

"Thanks to Allah," replied bin Laden.

The sheik informed bin Laden that another cleric had delivered a sermon in Saudi Arabia Sept. 11. "He said this was jihad and those people were not innocent victims," the sheik said, apparently referring to the victims of the World Trade Center and Pentagon attacks.

References to jihad, or holy war, and Allah run throughout the videotape, and at one point bin Laden recites a portion of verse: "I was ordered to fight the people until they say there is no god but Allah, and his prophet Muhammad."

Moments later, he said, "This event made people think [about true Islam], which benefitted Islam greatly," he said.

The approximately one-hour videotape was released Thursday after a team of four non-government translators brought in by the Pentagon listened to it to interpret bin Laden's Arabic and agree on a uniform version of his remarks. 

U.S. intelligence officers found the tape in a residence in Jalalabad. It bears a date stamp that says it was made Nov. 9.

The Pentagon offered a statement saying it released the tape after balancing "concerns about any additional pain that could be caused by its release against the value of having the world fully appreciate what we are up against in the war against terrorism."

"There was no doubt of bin Laden's responsibility for the Sept. 11 attacks before the tape was discovered," Defense Secretary Donald H. Rumsfeld said in the statement.

Numerous U.S. officials had already seen the tape prior to its release, and several members of the House and Senate intelligence committees had urged the Bush administration to release it.

The Associated Press contributed to this report.